| Abstract |
- The eighth annual report details continued progress on each of the five
objectives. In this year's report, Objectives II and III from previous
reports have been combined to reflect the similarity of each effort.
Improved fumigants: The previously established field trials continue to
demonstrate the superior performance of both chioropicrin and Vorlex after 18
years in poles and 13 years in piling. In addition, solid
methylisothiocyanate (MIT) continues to protect Douglas-fir poles in a manner
similar to Vorlex.
Along with evaluations of existing registered formulations, we continue
to explore the use of novel solid fumigants for their ability to arrest decay
in Douglas-fir heartwood. Laboratory studies indicate that both Mylone and
sodium n-methyldithiocarbamate (NaMDC) can be pelletized to improve handling
safety. Previous studies indicate that the rate of decomposition to produce
MIT is often too slow for effective fungal control, but the incorporation of
certain buffers or metallic salts can alter the rate and characteristics of
chemical decomposition. In our tests, the levels of chemical release varied
with PH; however, complete fungal control was not achieved. Further studies
are underway to determine if other conditions can alter the rate of MIT
production by these compounds. Both chemicals are registered for other, nonfood
uses and should be registerable for application to wood.
Efforts to better understand the properties of MIT, the major fungitoxic
product of both Vorlex and Vapam, are also continuing. These efforts have led
to the development of a preliminary model to describe fumigant movement
through Douglas-fir heartwood. The goal of this work is optimize treatment
dosage and application patterns for various pole sizes. In addition to the
more theoretical studies, we are continuing our efforts to determine the
ability of fumigants to control decay fungi in poles containing large decay
voids and to determine the levels of volatile emissions from fumigant treated
wood.
Field treatment: The field tests to evaluate potential replacements for
pentachlorophenol (penta) treatment of western redcedar sapwood were evaluated
after 7 years using the Aspergillus bioassay. The results indicate that
residual levels of chemical were detectable in the penta treatments, but the
remaining test chemicals exhibited little evidence of residual fungitoxicity.
Further decay tests are planned on material removed from these pole sections.
In addition to the pole sections, the small-scale test blocks were also
evaluated using the Aspergillus bioassay. The results indicate that several
chemicals remained in the wood at fungitoxic levels after one year of
accelerated weathering. Further decay tests are also planned on these
samples.
The bolt hole study is now in its seventh year and the incidence of decay
fungi in the test poles remains low. Variations in incidence from year to
year have made it difficult to draw any useful conclusions from this study.
To overcome this problem, a second test has been established which accelerates
leaching and evaluates the ability of a test fungus to invade the field
drilled bolt hole to cause wood weight loss.
Decay detection and residual strength: We continue to evaluate the use of
lectins for detecting fungal colonization at the early stages. This past
year, we completed a comparison of colonization by three common decay fungi
over a 12 week period.
The search for small-scale methods for estimating residual strength is
also continuing. Longitudinal compression measurements were used to determine
residual strength of a pole involved in an automobile accident.
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Finally, we have completed portions of a study to determine the effects
of fungal colonization on wood strength. Four fungi, Poria carbonica, Poria
placenta, Peniophora spp., and Haematostereum sanguinolentum were evaluated in
this study. Results with P. carbonica and Peniophora spp. indicate strength
effects lag behind fungal colony development in small beams. These results
were similar to previous field studies and indicate that air-seasoning for 2
to 3 years should not produce significant strength losses. Further studies
with these fungi are underway.
Initiation of decay in air-seasoning Douglas-fir: While the air-seasoning
studies are now completed, we are continuing to evaluate the data from these
tests. A detailed examination of the three year decay development study
indicates that several fungi were typically found only in the heartwood or
sapwood zones of the pole sections. In addition, the fungal flora at the four
seasoning sites varied widely, with the greatest deviation occurring at the
Oroville, CA. This site has the driest and warmest conditions, and would
appear to be best site for seasoning. A detailed discussion of isolation
frequency by position is presented for the eleven most common basidiomycetes.
Studies to prevent colonization by basidiomycetes during air-seasoning
are also continuing using polyborate dips or sprays. Sodium octaborate
tetrahydrate appears to reduce the level of colonization after one year of
air-seasoning at both Oroville and Corvallis, OR. Dipping shortly after
peeling appeared to produce the best results, although spraying at regular
intervals also had some effect on colonization. This study will continue for
an additional two years.
Determining the ability of existing pressure treatment cycles to
eliminate fungi which colonize Douglas-fir poles during air-seasoning also
remains a high priority. Only a few additional schedules were examined during
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the past year, but efforts to develop more realistic heating curves are under
way. In addition, several questions concerning the accuracy of the existing
data were answered. Additional studies using the Cellon process and the
longer steaming period for the ammoniacal copper zinc arsenate treatments are
planned in the coming year.
While sterilization during preservative treatment is an important factor
in pole longevity, questions have also arisen concerning the storage of poles
for long periods after treatment.
A survey of poles which were treated with creosote, pentachiorophenol,
chromated copper arsenate, and ammoniacal copper arsenate prior to storage for
one to 15 years was conducted. While colonization varied widely between
sites, the results indicated that storage of poles for long periods
substantially increased the risk that the pole would be placed in service with
an active decay fungus established somewhere along its length. Several
suggestions are made for remedying this situation.
Effect of microfunqi on Douglas-fir poles: A study was conducted to determine
the effect of microfungi which commonly colonize fumigant treated Douglas-fir
heartwood on the ability of P. carbonica and P. placenta to cause wood weight
loss in fumigant treated wood. The results indicate that several isolates
were associated with reduced weight losses by these fungi. The decreased
weight losses suggest that the microfungi could be colonizing fumigant treated
poles prior to the basidiomycetes and, once there, could help prevent
reinvasion. This scheme may help explain the remarkable protection provided
by fumigant treatment. Further studies are underway to explore this
possibility.
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